Alfalfa (Medicago sativa) is a forage crop grown primarily for its nutritive properties. Crude protein is the measure of the total nitrogen in a forage. It includes true plant proteins and non-protein nitrogen compounds, both of which are useable by ruminant animals. High protein content is the primary reason that legumes such as alfalfa are grown for forage. Another important measure of nutritive value for forage crops is how digestible the crop is. Acid detergent fiber (ADF) is that portion of the forage remaining after treatment with detergent under acidic conditions. ADF measures cellulose, lignin, and silica. As the value of ADF increases, the forage becomes less digestible. Lastly, nutritive value of the forage measured by percent total digestible nutrients (TDN) which is equal to the sum of percent digestible protein, percent digestible crude fiber, percent digestible starch and sugar and percent digestible fat.
Plant growth regulators (PGR's) are used in a wide variety of crops. There are a number of different types of PGR's, including anti-gibberellin, auxin-like, anti-auxins, and ethylenegenerators which have a wide ranging and unpredictable effect.
Prohexadione belongs to a new family of plant growth regulators (acylcyclohexanedione type plant growth regulators). These growth regulators block the biosynthesis of gibberellin (GA). Gibberellin is mainly responsible for controlling cell elongation. When gibberellin biosynthesis is blocked, plant cells will divide normally but the cells will be shorter. This results in shorter plants (reduced stature). Inhibitors of gibberillin biosynthesis are used in many crops to reduce stature, prevent lodging and the like. U.S. Pat. No. 4,560,403 describes prohexadione (3-hydroxy4-propionyl-5-oxo-3-cyclohexene carboxylic acid) and a number of other compounds of a class of cyclohexene plant growth regulators.
No information to date has been available on the actual effect of this new group of growth retardants, the acylcyclohexanediones, on alfalfa.
Plant growth regulators have been tested for further effects on the nutritive value and yield of alfalfa (Can. J. Plant Sci. 68:95-101). PGR's were tested from various classes of PGR's including anti-gibberellins; however, no acylcyclohexanedione types were tested. The results varied with all groups and appear to be total unpredictable, with both positive and negative neutral results both overall and for individual parameters. Within the anti-gibberellin group, both positive and negative effect were shown on ADF. In some cases, the results showed a complete reversal of effects in successive years. However, to date, none of the anti-gibberellin PGR's have shown a positive effect on total protein. So, while they have improved certain aspects of the nutritive value of alfalfa, none have improved all the parameters which comprise the nutritive value of alfalfa.
It appears that due to the lack of consistent results, both positive and negative, with plant growth regulators; the large number of compounds disclosed in the prior art; the lack of any test data in the art which would show the effects of prohexadione; the unpredictability of anti-gibberellin compounds on the art; the lack of any effect in total protein in the art that any reference is merely an invitation to experiment with these compounds in alfalfa.
It would be highly desirable that a PGR decrease ADF, increase TDN and increase Total Protein in alfalfa to improve the overall nutrient value of the alfalfa. It would be useful, in general, to accomplish this without significant crop injury that can occur with PGR applications; and to have the possibility of normal stature of the plant at some point after treatment.